How is fluid flow affected by surface roughness?

Surface roughness can increase fluid flow resistance and turbulence, reducing overall flow efficiency.

When a fluid flows over a surface, it experiences frictional forces due to the interaction between the fluid molecules and the surface. A smooth surface will offer less resistance to the fluid flow, resulting in a laminar flow with less turbulence. However, a rough surface will cause the fluid to experience more frictional forces, leading to a turbulent flow with increased energy dissipation.

The degree of surface roughness is commonly quantified using the Reynolds roughness parameter, which is the average height of surface irregularities relative to the fluid depth. As the Reynolds roughness parameter increases, so does the flow resistance and turbulence. This can be seen in applications such as pipe flow, where roughness can cause pressure drops and increased pumping costs.

Surface roughness can also affect the boundary layer of a fluid, which is the thin layer of fluid in contact with the surface. A rough surface can cause the boundary layer to become thicker and more turbulent, leading to increased drag and reduced flow efficiency.

In summary, surface roughness can significantly impact fluid flow by increasing resistance, causing turbulence, and affecting the boundary layer. Understanding these effects is important for designing efficient fluid systems and predicting flow behaviour.